Avoid reading inactive rowvals when computing the rank of a QRSparse (#…

…29925)

Fixes #29787

stdlib/SuiteSparse/src/spqr.jl

@@ -23,7 +23,7 @@ const ORDERING_BESTAMD = Int32(9) # try COLAMD and AMD; pick best#
 # tried.  If there is a high fill-in with AMD then try METIS(A'A) and take
 # the best of AMD and METIS. METIS is not tried if it isn't installed.
 
-using SparseArrays: SparseMatrixCSC
+using SparseArrays: SparseMatrixCSC, nnz
 using ..SuiteSparse.CHOLMOD
 using ..SuiteSparse.CHOLMOD: change_stype!, free!
 
@@ -342,7 +342,7 @@ end
 _ret_size(F::QRSparse, b::AbstractVector) = (size(F, 2),)
 _ret_size(F::QRSparse, B::AbstractMatrix) = (size(F, 2), size(B, 2))
 
-LinearAlgebra.rank(F::QRSparse) = maximum(F.R.rowval)
+LinearAlgebra.rank(F::QRSparse) = reduce(max, view(F.R.rowval, 1:nnz(F.R)), init = eltype(F.R.rowval)(0))
 
 function (\)(F::QRSparse{T}, B::VecOrMat{Complex{T}}) where T<:LinearAlgebra.BlasReal
 # |z1|z3|  reinterpret  |x1|x2|x3|x4|  transpose  |x1|y1|  reshape  |x1|y1|x3|y3|

stdlib/SuiteSparse/test/spqr.jl

@@ -93,4 +93,10 @@ end
     @test propertynames(F) == (:R, :Q, :prow, :pcol)
     @test propertynames(F, true) == (:R, :Q, :prow, :pcol, :factors, :τ, :cpiv, :rpivinv)
 end
+
+@testset "rank" begin
+    @test rank(qr(sprandn(10, 5, 1.0)*sprandn(5, 10, 1.0))) == 5
+    @test all(iszero, (rank(qr(spzeros(10, i))) for i in 1:10))
+end
+
 end